Previous methods of producing linear polydichlorophosphazene polymers centered around batch processes in which the cyclic trimer (Cl.sub.2 PN).sub.3 is converted to high molecular weight polymers via hydrolytic polymerization as disclosed in U.S. Pat. Nos. 3,515,688 and 3,370,020. The trimer is produced by reacting PCl.sub.5 and NH.sub.4 Cl followed by careful purification. The costs of preparation and the purification of cyclic trimer, (Cl.sub.2 PN).sub.3, may be avoided by a direct synthesis route, such that the final cost of producing substituted polyphosphazes, particularly for floor coatings and foams may be greatly reduced. It has previously been deemed impossible to directly polymerize PCl.sub.5 and NH.sub.4 Cl to produce linear polydichlorophosphazene. The only reported preparation of (PCl.sub.2 N)x from PCl.sub.5 and NH.sub.4 Cl was in Polvmer 11, pages 31, 43 (1970) which describes the accidental preparation of a soluble chloropolymer.